Japan lodged a formal protest with China on Thursday after detecting a Chinese frigate and an unidentified foreign submarine in waters close to the disputed Senkaku Islands in the East China Sea.
The Japan Self-Defence Forces -- the country's military -- spotted the Jiangkai II-class frigate at around 11 a.m., close to the Senkaku islands, a group of uninhabited islands controlled by Japan, although it did not enter Japanese territorial waters, Efe news agency reported.
Vice Foreign Minister Shinsuke Sugiyama summoned Chinese Ambassador to Japan Cheng Yonghua on Thursday to express his grave concern regarding the issue and protest the frigate's entry into the area, the Japanese Foreign Ministry said.
A foreign submarine was also detected in the contiguous waters near Japanese territory on Wednesday and Thursday, said the country's Defence Ministry, which believes that the submarine is also from China, as reported by local news agency Kyodo.
The last time a foreign submarine was spotted in Japanese contiguous waters was in February 2016.
Tokyo has been in a territorial dispute with Beijing over the sovereignty of the Senkaku Islands -- known as Diaoyu Islands in China -- which has intensified since the former in 2012 nationalised three of the islets.
Located around 150 km northeast of Taiwan, the uninhabited Senkaku Islands have an area of about 7 sq km and are said to possibly be rich in marine and energy resources.
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(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)